I. Field
The following description relates generally to wireless communications, and more particularly to an improved uplink pilot.
II. Background
Wireless communication systems are widely deployed to provide various types of communication; for instance, voice and/or data may be provided via such wireless communication systems. A typical wireless communication system, or network, can provide multiple users access to one or more shared resources. For instance, these systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, lime division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, and orthogonal frequency division multiple access (OFDMA) systems.
Coherent demodulation of a data channels typically relies on the derivation of the phase and amplitude changes introduced by the transmission link. Generally, higher data rates on a transmission link require a better phase and amplitude reference in order to perform well. This amplitude and phase reference is usually given by a pilot sequence or channel.
As an example, a data rate of sixteen (16) kilo-bits per second (Kb/s) transmitted the uplink of W-CDMA will require a pilot channel with a signal-to-noise ratio (SNR) of approximately Ec/Nt=−20 dB. On the other hand, if the data rate is increased to eleven (11) mega-bits per second (Mbit/s) the signal-to-noise ratio of the channel carrying the pilot (denoted “dedicated physical control channel”, or DPCCH) should be approximately Ec/Nt=−2 dB. This higher SNR can be achieved by increasing the transmit power of the DPCCH at the transmitter.
Current and prior releases of W-CDMA do not allow the possibility for the user equipment (UE) to autonomously vary the transmit power of the pilot channel in order to accommodate an increase in the transmitted data rate, thus leading to inefficiencies. With the introduction of even higher data rates on the uplink (UL) in contemplated future releases of W-CDMA and other systems, these inefficiencies can be more significant, barring support for the communication of high data rates.
With current practices, the up and down commands issued by the inner-loop of the fast power control is based on the SNR measure on the pilot bits at the base station. Unfortunately, current deployments of base stations in current versions of W-CDMA cannot differentiate the following from each other: a) an increase in the transmit power of the DPCCH initiated by the UE (i.e., because of the high data rate transmission), and b) an improvement in the radio link (better path loss, reduction in interference level). In both scenarios the systems observe that the SNR of the pilot is increased beyond the target SNR, and issue a down command. The correct behavior would be for the base station to only issue a down command for the case where there is an improvement in the radio link.
Moreover, with current practices, when the bases stations issue a down command in the case of an increase in the transmit power of the DPCCH, the base station operates to effectively reduce the SNR for the high data rate transmission and thereby degrades its performance. Furthermore, with current practices, after the UE has finished transmitting the high rate packet, improved efficiencies (e.g., boost) in the pilot transmit power will be removed since the UE, having executed the undesirable down commands, results in a pilot with a low SNR such that lower data rate transmissions can fail.
From the foregoing, it is appreciated that there exists a need for system and methods to ameliorate the shortcomings of existing practices.